Programmed I/O vs interrupt-driven I/O in Operating Systems - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the sentence to describe Programmed I/O.

Operating Systems

In Programmed I/O, the CPU [1] the device status continuously to check if it is ready.

Drag options to blanks, or click blank then click option'

Apolls

Bignores

Cinterrupts

Dsleeps

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing polling with interrupts.

Thinking the CPU sleeps while waiting.

Programmed I/O uses polling, where the CPU repeatedly checks the device status.

2fill in blank

medium

Complete the sentence to describe interrupt-driven I/O.

Operating Systems

In interrupt-driven I/O, the device [1] the CPU when it is ready to transfer data.

Drag options to blanks, or click blank then click option'

Aignores

Bpolls

Cinterrupts

Dwaits

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up who initiates communication.

Thinking the CPU polls in interrupt-driven I/O.

Interrupt-driven I/O uses interrupts where the device signals the CPU when ready.

3fill in blank

hard

Fix the error in the statement about CPU usage in Programmed I/O.

Operating Systems

Programmed I/O is inefficient because the CPU [1] while waiting for the device.

Drag options to blanks, or click blank then click option'

Asleeps

Binterrupts

Cignores

Dpolls

Attempts:

3 left

💡 Hint

Common Mistakes

Saying the CPU sleeps or ignores the device.

Confusing polling with interrupts.

The CPU wastes time polling the device repeatedly, making Programmed I/O inefficient.

4fill in blank

hard

Fill both blanks to complete the comparison between Programmed I/O and interrupt-driven I/O.

Operating Systems

Programmed I/O uses [1] to check device status, while interrupt-driven I/O uses [2] to notify the CPU.

Drag options to blanks, or click blank then click option'

Apolling

BDMA

Cinterrupts

Dbuffers

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing DMA with interrupts.

Mixing polling and buffering concepts.

Programmed I/O uses polling; interrupt-driven I/O uses interrupts to signal the CPU.

5fill in blank

hard

Fill all three blanks to complete the dictionary describing I/O methods.

Operating Systems

io_methods = {"Programmed I/O": "CPU [1] device status", "Interrupt-driven I/O": "Device [2] CPU", "DMA": "Direct data transfer without [3] CPU intervention"}

Drag options to blanks, or click blank then click option'

Apolls

Binterrupts

Cconstant

Dbuffers

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up who polls and who interrupts.

Misunderstanding DMA's role.

Programmed I/O: CPU polls device status.
Interrupt-driven I/O: Device interrupts CPU.
DMA: Direct data transfer without constant CPU intervention.

Practice

1. Which of the following best describes programmed I/O?

easy

A. CPU ignores the device until a scheduled time

B. Device sends a signal to CPU only when it needs attention

C. CPU and device communicate using direct memory access

D. CPU continuously checks the device status until it is ready

Solution

1. Step 1: Understand programmed I/O behavior

   Programmed I/O means the CPU actively checks the device repeatedly to see if it is ready.

2. Step 2: Compare options with definition

   CPU continuously checks the device status until it is ready matches this behavior exactly, while others describe interrupt or other methods.

3. Final Answer:

   CPU continuously checks the device status until it is ready -> Option D

4. Quick Check:

   Programmed I/O = CPU polls device [OK]

Hint: Programmed I/O means CPU keeps checking device status [OK]

Common Mistakes:

• Confusing programmed I/O with interrupt-driven I/O
• Thinking device signals CPU in programmed I/O
• Mixing up direct memory access with programmed I/O

2. Which of the following is the correct statement about interrupt-driven I/O?

easy

A. Device interrupts CPU only when it needs service

B. CPU waits in a loop checking device status

C. CPU ignores device signals completely

D. CPU uses programmed polling to check device

Solution

1. Step 1: Recall interrupt-driven I/O definition

   Interrupt-driven I/O means the device sends a signal (interrupt) to the CPU when it needs attention.

2. Step 2: Match options to definition

   Device interrupts CPU only when it needs service correctly states that the device interrupts the CPU only when service is needed.

3. Final Answer:

   Device interrupts CPU only when it needs service -> Option A

4. Quick Check:

   Interrupt-driven I/O = device signals CPU [OK]

Hint: Interrupt-driven means device signals CPU when ready [OK]

Common Mistakes:

• Choosing options describing CPU polling
• Assuming CPU ignores device signals
• Confusing programmed I/O with interrupt-driven I/O

3. Consider this scenario: A CPU uses programmed I/O to read data from a device. What is the main effect on CPU usage?

medium

A. CPU can perform other tasks while waiting for device

B. CPU is busy checking device status and cannot do other work

C. CPU ignores the device until data is ready

D. CPU receives an interrupt when device is ready

Solution

1. Step 1: Understand CPU behavior in programmed I/O

   In programmed I/O, CPU repeatedly checks device status, which keeps it busy and unable to do other tasks efficiently.

2. Step 2: Analyze options for CPU usage

   CPU is busy checking device status and cannot do other work correctly states CPU is busy polling and cannot perform other work effectively.

3. Final Answer:

   CPU is busy checking device status and cannot do other work -> Option B

4. Quick Check:

   Programmed I/O = CPU busy polling device [OK]

Hint: Programmed I/O keeps CPU busy waiting, no multitasking [OK]

Common Mistakes:

• Thinking CPU can multitask during programmed I/O
• Confusing interrupt-driven I/O effects with programmed I/O
• Assuming CPU ignores device in programmed I/O

4. A system uses interrupt-driven I/O but the CPU never responds to device interrupts. What is the likely problem?

medium

A. Interrupts are disabled or masked in the CPU

B. CPU is using programmed I/O instead

C. Device is not sending any interrupts

D. CPU is stuck in a loop polling the device

Solution

1. Step 1: Identify why CPU ignores interrupts

   If CPU never responds to interrupts, a common cause is that interrupts are disabled or masked, preventing CPU from handling them.

2. Step 2: Evaluate other options

   Interrupts are disabled or masked in the CPU correctly identifies this cause. Other options either contradict the interrupt-driven setup or describe different issues.

3. Final Answer:

   Interrupts are disabled or masked in the CPU -> Option A

4. Quick Check:

   CPU ignoring interrupts = interrupts disabled [OK]

Hint: CPU ignoring interrupts usually means interrupts are disabled [OK]

Common Mistakes:

• Assuming device is not sending interrupts
• Confusing programmed I/O with interrupt-driven I/O
• Thinking CPU polls device in interrupt-driven mode

5. A system designer wants to maximize CPU efficiency while handling multiple I/O devices. Which approach is best and why?

hard

A. Use programmed I/O because CPU controls all device checks

B. Use programmed I/O with longer polling intervals to reduce CPU load

C. Use interrupt-driven I/O so CPU works on other tasks until interrupted

D. Use neither; rely on manual device checks by the user

Solution

1. Step 1: Analyze CPU efficiency needs

   Maximizing CPU efficiency means CPU should not waste time waiting or polling devices unnecessarily.

2. Step 2: Compare I/O methods for efficiency

   Interrupt-driven I/O allows CPU to do other work and only respond when device signals, improving efficiency.

3. Step 3: Evaluate other options

   Programmed I/O wastes CPU cycles; manual checks are impractical. Longer polling reduces load but still wastes CPU time.

4. Final Answer:

   Use interrupt-driven I/O so CPU works on other tasks until interrupted -> Option C

5. Quick Check:

   Interrupt-driven I/O maximizes CPU efficiency [OK]

Hint: Interrupt-driven I/O lets CPU multitask efficiently [OK]

Common Mistakes:

• Choosing programmed I/O for efficiency
• Ignoring CPU multitasking benefits
• Thinking manual checks improve performance